1. Field of the Invention
The present invention relates to an apparatus and a method for enhancing image contrast; more particularly, it relates to an apparatus and a method for enhancing image contrast by adjusting an illumination level of a light source according to a plurality of thresholds.
2. Descriptions of Related Art
Since display apparatuses are in great demand today, providers are constantly trying to improve the qualities of the display apparatuses to earn more market share, wherein image contrast is one of the quality factors in need of improvement. A display apparatus with a higher contrast has the capability to display images in a better quality. This means that the display apparatus with higher contrast displays images in a wider range of brightness. Therefore, improvement of the level of contrast is an important consideration when trying to advance display apparatuses.
Both U.S. Pat. Nos. 6,831,722 and 6,867,834 provide a method for increasing contrast. As disclosed in the specifications, both of them require several optical materials and modules to match the polarity of output lights in order to achieve the objects of brightness adjustment and contrast enhancement. In addition to the requirements of complex optical and manufacturing techniques, the methods are limited to LCDs, and cannot be applied to the display systems of digital light processing (DLP).
U.S. Pat. No. 6,683,657 discloses an optical modulator that changes brightness and increases contrast. The optical modulator includes an ultrasonic motor placed between a lighting module and an optical module. This kind of structure increases the cost and complexity of projection devices. Moreover, U.S. Pat. No. 5,467,146 also discloses an optical modulator to change brightness and to increase contrast. The latter patent further needs an optical shutter to achieve the object of contrast enhancement. Similarly, the cost and complexity of projection devices will increase consequently.
U.S. Pat. No. 6,873,742 also provides a signal processing technique to increase brightness of a comparatively bright part and decrease brightness of a comparatively dark part by processing a brightness value of a digital image data based on an algorithm. Contrast is hence enhanced. However, the original information in the digital image data is distorted due to the signal processing.
In conclusion, the apparatuses or the methods of the prior art for enhancing contrast of images result in either an increase in cost and manufacturing complexity or the distortion of images. Therefore, an economical solution for enhancing contrast of display apparatuses is still desired.